Based on the principle of differential pressure capacitance, the sensing element is a tensioned metal diaphragm located at an equal distance between two fixed metal surfaces. Three plates form a pair of complementary capacitors. The electrically insulating filling fluid (usually liquid silicon) transfers movement from the isolation diaphragm to the sensing diaphragm, and can also serve as an effective medium for two capacitors:

Any pressure difference between the units will cause the diaphragm to bend in the direction of the minimum pressure. The sensing diaphragm is a precision manufactured spring element, which means its displacement is a predictable function of the applied force. In this case, according to the standard force-pressure-area equation f=pa, the applied force can only be a function of the pressure difference acting on the surface of the diaphragm.

In this case, two forces are caused by the pressure interaction of the two fluids, so the force-pressure area equation can be rewritten to describe the resultant force as a function of the pressure difference (p1-p2) and the diaphragm area: f=( p1-p2) a. Since the diaphragm area is constant, and the force is predictably related to the diaphragm displacement. Now, what we need is to accurately measure the displacement of the diaphragm to infer the pressure difference.